title: In situ study of atomic structure transformations of Pt-Ni nanoparticle catalysts during electrochemical potential cycling.
abstract: When exposed to corrosive anodic electrochemical environments, Pt alloy nanoparticles (NPs) undergo selective dissolution of the less noble component, resulting in catalytically active bimetallic Pt-rich core-shell structures. Structural evolution of PtNi6 and PtNi3 NP catalysts during their electrochemical activation and catalysis was studied by in situ anomalous small-angle X-ray scattering to obtain insight in element-specific particle size evolution and time-resolved insight in the intraparticle structure evolution. Ex situ high-energy X-ray diffraction coupled with pair distribution function analysis was employed to obtain detailed information on the atomic-scale ordering, particle phases, structural coherence lengths, and particle segregation. Our studies reveal a spontaneous electrochemically induced formation of PtNi particles of ordered Au3Cu-type alloy structures from disordered alloy phases (solid solutions) concomitant with surface Ni dissolution, which is coupled to spontaneous residual Ni metal segregation during the activation of PtNi6. Pt-enriched core-shell structures were not formed using the studied Ni-rich nanoparticle precursors. In contrast, disordered PtNi3 alloy nanoparticles lose Ni more rapidly, forming Pt-enriched core-shell structures with superior catalytic activity. Our X-ray scattering results are confirmed by STEM/EELS results on similar nanoparticles.
authors.affiliation: Technical University Berlin, Strasse des 17. Juni 124, 10623 Berlin, Germany. x.tuaev@utwente.nl
authors.forename: Xenia
authors.initials: X
authors.lastname: Tuaev
authors.forename: Stefan
authors.initials: S
authors.lastname: Rudi
authors.forename: Valeri
authors.initials: V
authors.lastname: Petkov
authors.forename: Armin
authors.initials: A
authors.lastname: Hoell
authors.forename: Peter
authors.initials: P
authors.lastname: Strasser
mesh_terms: D000497:Alloys / Q000737:chemistry / Q000528:radiation effects; D004574:Electromagnetic Fields; D046911:Macromolecular Substances / Q000737:chemistry / Q000528:radiation effects; D008422:Materials Testing; D008968:Molecular Conformation / Q000528:radiation effects; D009532:Nickel / Q000737:chemistry* / Q000528:radiation effects*; D010316:Particle Size; D010984:Platinum / Q000737:chemistry* / Q000528:radiation effects*; D013499:Surface Properties / Q000528:radiation effects
chemical_list: D000497:Alloys; D046911:Macromolecular Substances; D010984:Platinum; D009532:Nickel